In such a system it is extremely desirable that the reference voltage identically fed to all components be virtually invariable, i.e. substantially unaffected by changes in supply voltage and temperature. Another important requirement is to prevent so-called cross-talk among the several components, i.e. mutual interference in their operations, even when their reference potentials or biasing voltages are delivered by a common source.
An article titled "Fully Compensated Emitter-Coupled Logic: Eliminating the Drawbacks of Conventional ECL" by Harold H. Muller et al, published October 1973, IEEE Journal of Solid-State Circuits, Vol. SC-8, No. 5, pages 362-367, describes a circuit arrangement with a multiplicity of transistors--mostly of NPN conductivity type--generating stabilized voltages which are substantially invariant over wide ranges of ambient temperature and supply voltage. The transistors draw high currents and no means are included for feeding programmable currents to other circuit components.
Biasing circuits for ECL line drivers and receivers, marketed under the designation F10K by Fairchild Industries, do not generate stable reference voltages or programmable currents. Such programmability is provided in a biasing circuit marketed under the designation LH146 by National Semiconductors Corp.; there, too, no stabilized voltages are generated and the emitter currents are affected by variations in the supply voltage.
A particular instance of circuit components requiring fixed biasing voltages and preferably programmable operating currents are transceivers connected across outgoing transmission lines as described in commonly owned U.S. patent application Ser. No. 552,499 filed Nov. 17, 1983 by Piero Belforte (now U.S. Pat. No. 4,593,211 issued June 3, 1986). In such a transceiver, an input stage comprises a pair of control transistors connected to a pair of driving transistors in an output stage, the two latter transistors being alternately connectable through a main constant-current generator across the associated transmission line in dependence upon an incoming signal applied to one of the control transistors. The input stage further includes an ancillary constant-current generator feeding the two control transistors while two other constant-current generators in the output stage serve to maintain the inactive driving transistors is performed by a further transistor pair. The several ancillary current generators deliver only small currents, compared with the line current supplied by the main generator, and are under the control of fixed biasing voltages. The transceiver may be part of a full-duplex transmission system of the type disclosed in commonly owned U.S. Pat. No. 4,393,494 in the names of Piero Belforte et al.